1. Field of the Invention
The present invention relates generally to audio processing, and more particularly to reducing noise and echo within an acoustic signal.
2. Description of Related Art
Various types of audio devices such as cellular phones, phone handsets, headsets, and conferencing systems can suffer from the problem of acoustic echo, which is a delayed and distorted version of an original sound reflected back to its source. In a typical conversation, a far-end acoustic signal of a remote person speaking at the “far-end” is transmitted over a network to an audio device of a person listening at the “near-end.” When the far-end acoustic signal is presented through a speaker of the audio device, an acoustic wave is generated within the near-end acoustic environment. Part of this acoustic wave may be reflected via an echo path to a microphone or other acoustic sensor of the audio device. This reflected signal may then be processed by the audio device and transmitted back to the remote person, resulting in echo. As such, the remote person will hear a delayed and distorted version of their own speech, which can interfere with normal communication and is annoying.
In order to reduce or eliminate this echo, an acoustic echo canceller may be utilized in the audio device. The far-end acoustic signal may be used by the acoustic echo canceller to predict the echo within the near-end acoustic signal received by the microphone. Typically, a transfer function is modeled to predict the echo path from the speaker to the microphone. Echo cancellation can then be performed in the waveform domain, whereby the echo is predicted, inverted, delayed, and subtracted out of the near-end acoustic signal.
Since the near-end acoustic environment is rarely fixed, the echo path is typically constantly changing. As a result, the acoustic echo canceller is continually updating the transfer function used to model the echo path. Errors in the echo prediction usually occur due to the difficultly in accurately modeling the changing environment. If the transfer function is even slightly incorrect, or an applied delay is incorrect, echo will remain in the near-end acoustic signal.
This echo can be problematic for a noise reduction system within the audio device. The noise reduction system is used to reduce background noise within the near-end acoustic signal to improve voice and/or call quality. The noise reduction system may extract and track speech characteristics such as pitch and level in the near-end acoustic signal to build near-end speech and noise models. These speech and noise models are used to generate a signal modification that preserves the desired near-end speech signal and suppresses the unwanted near-end noise signals.
However, for applications such as teleconferencing and other hand-free communication scenarios, the echo can also possess strong speech characteristics such as high pitch saliency and level. As a result, the echo may appear to be another speech source to the noise reduction system. Consequently, the noise reduction system may mistakenly adapt its speech and noise models to the echo, resulting in damaged speech or echo leakage in the processed signal.
It is therefore desirable to provide noise and echo reduction techniques which can increase the quality and responsiveness of noise reduction systems.